Friday, April 4, 2014

An elderly woman with h/o diabetes and hypertension but no prior cardiac history had been having exertional chest pain for months, though with a normal stress test. She had onset at rest of severe substernal chest pressure radiating to the neck. There was associated SOB and diaphoresis. EMS came and recorded this ECG:

What is it? See annotated ECG below.

I have put arrows where I think the P-waves are. They march out regularly, but are non-conducting. This is complete, 3rd degree, AV block. The escape is regular at a rate of about 36 and looks like a right bundle branch block and left anterior fascicular block, which means that the escape originatesfrom the posterior fascicle. (Another possibility would be junctional escape with RBBB/LAFB, but this should be faster). There are no clear ischemic ST segments or T-waves, though the expected discordant ST depression in V2 is not there, and there is a hint of upwardly sloping ST elevation in V1.

She received nitroglycerin and aspirin and her pain very much improved. She arrived in the ED with a pulse of 81 and very elevated BP at 200/90.

This ECG was recorded:

Now there is sinus rhythm with LBBB. The only hint of ischemia are concordant T-waves in V5 and V6 (these were quite specific for MI - but not STEMI - in Sgarbossa's study). This ECG also confirms that the previous escape was NOT junctional because nodal escape would also have associated LBBB.

The transcutaneous pacer was placed, she was given clopidogrel and heparin, and the cath lab was activated. Electrolytes and CBC were normal. A formal echo was done which showed an anterior and apical wall motion abnormality consistent with LAD ischemia. The EF was about 40%.

She became bradycardic again and this was recorded:

The first half of the ECG has second degree block Mobitz II (by ECG alone, this could be Mobitz I; but in this clinical context, with previous complete AV block, it must be Mobitz II), then changing to normal rhythm with every P-wave conducted. All conducted beats have LBBB morphology and there is no clear evidence of ischemia.

Here is a third ED ECG:

There is 2:1 AVblock for 3 beats, with every 2nd P-wave conducting to LBBB. Then there are 3 P-waves that do not conduct, followed by an RBBB escape (just like on the prehospital ECG). Then 2:1 block resumes.

The patient went to cath and had severe 3 vessel disease. She ruled out for MI!! Maximum troponin I was 0.016 ng/mL (99% reference = 0.030 ng/mL.

She had a pacer placed and went for CABG, successful. Here is her paced ECG after surgery:

Paced rhythm with no evidence of ischemia

Later, she was in sinus rhythm:

Sinus with LBBB, again, no ischemia.

Lessons:

1. Ischemia can be severe enough to result in low EF, wall motion abnormality, and heart block, but with negative troponins.
2. There are other indications for the cath lab than ST segment or T-wave abnormalities. These include hemodynamic instability, heart failure, dysrhythmias, heart block, and ischemic chest pain that cannot be controlled by medical means.

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